This invention relates generally to collet support of work, such as machine tool shafts or shanks, and more particularly to fine adjustment of such shanks, as during connection and disconnection of tool shanks to and from collets.
Connection of machine tool shanks, as for example milling tool shanks, to collets for support during rotary milling, requires that the collets be precision connected to the rotary bodies of tool holders. This requires accurate, forcible, axial displacement, i.e., jamming, of conical portions of collets into conical bores of such holders, for frictional interconnection. A high degree of axial force is thereby required; and, when the tool shank is to be removed, a high degree of collet extraction axial force is required to break the frictional interconnection.
Originally, tool holders were simple side locking devices, with set screws pushing a tool to one side to hold it in place. Next came various collet and chuck methods to hold tools. The more recent versions of these use complicated hydraulic or mechanical devices to try to hold the tool fixed coaxially. The most recent means for doing this is to shrink fit the tool in the holder body.
A side lock holder is deficient for coaxiality and fixity. Collet devices are more advantageous for coaxial holding, but less advantageous for fixity. Chucks in general are acceptable for coaxial holding, but are deficient for fixity because they employ thin sections in order to collapse, even with the more sophisticated hydraulic or milling chucks.
The shrink fit holder has drawbacks related to requiring 400-degree temperature, and hand loading a tool. Heating cycles are limited because the tool tends to lose its memory. Also, tool removal is a major problem whether done by reheating or mechanical means. In smaller sizes the tool tends to come loose and move in the holder because of the limited compression available from shrink fitting.
Another factor which affects the shrink fit holder is the finish on the mating surfaces. A rougher surface is desirable in order to prevent slippage; however, a rough surface will not last as long as desirable, before it begins to wear, causing a loss of grip.
There is need for an improved tool holder that will overcome problems, as referred to.